黄土高原油松冠层气孔导度和蒸腾变化特征与模拟

油松是黄土高原重要的造林树种，模拟其冠层气孔导度和蒸腾对区域水量平衡计算和人工林可持续经营具有重要意义。基于2015-2018年TDP （Thermal dissipation probes）方法所测得液流数据，分析了黄土高原地区油松冠层平均气孔导度（g_c）与冠层蒸腾（Tr）的变化特征与影响因素，并采用Penman-Monteith公式和Jarvis型气孔导度模型模拟了其g_c和Tr的变化过程，结果表明：（1）该地区油松g_c和Tr日内变化均呈现单峰型，日均蒸腾耗水量为（1.25±0.57） mm/d，生长季（4-10月）总蒸腾耗水量均值为195.47 mm。（2）g_c的日内变化受太阳辐射（Rad）驱动（偏相关系数为0.65），当Rad高于300 W/m²时，驱动作用减弱；g_c的日内变化受水汽压亏缺（VPD）控制（偏相关系数为-0.41），随VPD的增加而降低；g_c的日际变化受土壤水分限制（偏相关系数为0.46），当根区相对有效含水率（REW）低于0.45时，限制作用明显。（3）结合Penman-Monteith公式与Jarvis型模型能有效模拟黄土高原油松g_c与Tr变化，小时尺度g_c与Tr模拟的纳什效率系数（NSE）分别为0.80和0.78，日尺度Tr模拟的NSE为0.76。

Characteristics and modeling of canopy stomatal conductance and transpiration of Pinus tabuliformis on the Loess Plateau

Pinus tabuliformis is an important afforestation tree species on the Loess Plateau. Accurate estimation of its canopy stomatal conductance and transpiration is of great significance for regional water balance and sustainable forest management. Previous studies have simulated the daily variation of the transpiration of Pinus tabuliformis based on the response of its stomatal conductance to environmental factors, but the influence of soil moisture has not been considered. Soil moisture is one of the most important factors that limit plant transpiration in this region. Considering the response of stomatal conductance to soil moisture is crucial for modeling transpiration. To estimate the transpiration of Pinus tabulaeformis, the trunk sap flow velocity was measured by the thermal dissipation probes (TDP) method from 2015 to 2018. The meteorological factors and soil moisture were also monitored simultaneously. We analyzed the characteristics and controlling factors of the mean canopy stomatal conductance (g_c) and transpiration (Tr) of Pinus tabuliformis on the Loess Plateau. Then the Penman-Monteith formula and Jarvis-type stomatal conductance model were used to simulate the process of its g_c and Tr. The results showed that:(1) The daily variation of g_c and Tr displayed a unimodal curve. The average daily transpiration rate of Pinus tabuliformis was (1.25±0.57) mm/d, and the mean annual total water consumption in the growing season (April to October) was 195.47 mm. (2) Solar radiation (Rad) was the main driving factor of the diurnal variation of g_c (the partial correlation coefficient was 0.65), while the driving effect was weakened when the Rad was higher than 300 W/m². Vapor pressure deficit (VPD) was the main controlling factor of g_c diurnal variation (the partial correlation coefficient was -0.41) and g_c decreased with the increase of VPD. Soil moisture was the main limiting factor of the daily variation of g_c (the partial correlation coefficient was -0.46). When the relative extractable water content (REW) of the root zone was lower than 0.42, g_c would decrease rapidly with the decrease of soil moisture. (3) Combining the Penman-Monteith formula and Jarvis-type model could accurately simulate the variation of g_c and Tr. The Nash-Sutcliffe efficiency coefficient (NSE) of hourly g_c and Tr simulations were 0.80 and 0.78, respectively, while the NSE of daily Tr simulation was 0.76. The parameters of the model obtained in this study were consistent with the basic characteristics of drought tolerance of Pinus tabuliformis, and could provide an important reference for evaluating the canopy stomatal conductance and transpiration variation of the Pinus tabuliformis on the Loess Plateau.